1. Field of the Invention
The present invention relates to a compound planetary gear mechanism.
2. Discussion of the Background
Compound planetary gear mechanisms are equipped with a plurality of planetary gear mechanisms and are in use in a variety of fields in that the plurality of planetary gear mechanisms realize high rotation ratio (high reduction gear ratio or high speed-increasing ratio) that is difficult to realize by a single planetary gear mechanism. Conventional compound planetary gear mechanisms are disclosed in, for example, WO2007/017935 and Japanese Unexamined Patent Application Publication No. 2008-275112.
The compound planetary gear mechanism according to WO2007/017935 includes two planetary gear mechanisms coupled to one another. Each planetary gear mechanism includes a sun gear and two planetary gears. The sun gear and two planetary gears of each planetary gear mechanism are coaxial to and integral with the respective, corresponding sun gear and two planetary gears of the other planetary gear mechanism. Likewise, the compound planetary gear mechanism according to Japanese Unexamined Patent Application Publication No. 2008-275112 includes two planetary gear mechanisms coupled to one another. One of the two planetary gear mechanisms includes a plurality of planetary gears disposed in a nonaxisymmetric manner.